Electricity gets the bulk of the attention in clean-energy discourse (this newsletter is, after all, called Volts) but half of global final energy consumption comes in the form not of electricity, but of heat. When it comes to reaching net zero emissions, heat is half the problem.
Roughly half of heat is used for space and water heating, which I have covered on other pods. The other half — a quarter of all energy humans use — is found in high-temperature industrial processes, everything from manufacturing dog food to making steel or cement.
The vast bulk of industrial heat today is provided by fossil fuels, usually natural gas or specialized forms of coal. Conventional wisdom has had it that these sectors are “difficult to decarbonize” because alternatives are either more expensive or nowhere to be found. Indeed, when I covered an exhaustive report on industrial heat back in 2019, the conclusion was that the cheapest decarbonization option was probably CCS, capturing carbon post-combustion and burying it.
A lot has changed in the last few years. Most notably, renewable energy has gotten extremely cheap, which makes it an attractive source of heat. However, it is variable, while industrial processes cannot afford to start and stop. Enter the thermal battery, a way to store clean electricity as heat until it is needed.
A new class of battery — “rocks in a box” — stores renewable energy as heat in a variety of different materials from sand to graphite, delivering a steady supply to various end uses. One of the more promising companies in this area is Rondo, which makes a battery that stores heat in bricks.
I talked with Rondo CEO John O'Donnell about the importance of heat in the clean-energy discussion, the technological changes that have made thermal storage viable, and the enormous future opportunities for clean heat and a renewables-based grid to grow together.
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